Disk drive device with hub

ABSTRACT

The disk drive device includes a base member, a hub, a bearing unit which is arranged on the base member and which rotatably supports the hub, and a spindle drive unit which drives the hub to rotate. The spindle drive unit includes a stator core having a salient pole, a coil wound around the salient pole and a magnet opposed to the salient pole. The hub formed of magnetic material includes an outer cylinder portion engaged with an inner circumference of a recording disk and an inner cylinder portion to which an outer circumference of the magnet is fixed. The diameter of the inner cylinder portion is larger than the diameter of the outer cylinder portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk drive device having a hub on which a recording disk is mounted.

2. Description of the Related Art

Recently, a disk drive device such as an HDD has been improved in bearing stiffness by incorporating a dynamic pressure fluid bearing unit. There is a case that such a disk drive device having the dynamic pressure fluid bearing unit is mounted on a small portable apparatus. A portable apparatus is desired to be further thinned and lightened. Therefore, the disk drive device which is mounted on the portable apparatus is desired to be further thinned and lightened.

For example, patent document 1 has disclosed a disk drive device having a dynamic pressure fluid bearing unit with a first radial dynamic pressure groove of which formed width in the axial direction is narrower than that of a second radial dynamic pressure groove.

Patent document 1: Japanese Patent Application Laid-Open No. 2007-198555

In order to thin a disk drive device, it is necessary to thin a spindle drive unit and dynamic pressure fluid bearing unit. Here, when the spindle drive unit is further thinned, there may be a case that rotation becomes unstable due to torque decrease. Further, when the dynamic pressure fluid bearing unit is further thinned, there may be a case that rotation becomes unstable due to decrease in stiffness of the dynamic pressure fluid bearing unit. When the rotation becomes unstable as mentioned above, there may be a case that normal reading/writing operation of magnetic data cannot be performed at worst.

SUMMARY OF THE INVENTION

The present invention is devised in view of the abovementioned situation and a purpose thereof is to provide a disk drive device which stably rotates a recording disk while being further thinned.

In view of the abovementioned, a disk drive device according to an aspect of the present invention includes a base member, a hub, a bearing unit which is arranged on the base member and which rotatably supports the hub, and a spindle drive unit which drive the hub to rotate. The spindle drive unit includes a stator core having a salient pole, a coil wound around the salient pole and a magnet opposed to the salient pole. The hub formed of magnetic material includes an outer cylinder portion engaged with an inner circumference of a recording disk and an inner cylinder portion to which an outer circumference of the magnet is fixed. The diameter of the inner cylinder portion is larger than the diameter of the outer cylinder portion.

According to this aspect, the diameter of the magnet can be larger than the inner circumference of the recording disk by setting the diameter of the inner cylinder portion to be larger than that of the outer cylinder portion. Thus, even with the thinned disk drive device, the magnet can be ensured to be sufficient size so as to suppress torque decrease. Accordingly, the rotation of the recording disk can be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures.

FIG. 1A is a view illustrating a disk drive device according to an embodiment.

FIG. 1B is a view illustrating the disk drive device according to the present embodiment.

FIG. 2 is a sectional view of a part of the disk drive device according to the present embodiment.

FIG. 3 is a sectional view of a hub according to the present embodiment.

FIG. 4 is a sectional view of a part of a disk drive device according to the related art.

FIG. 5A is a view illustrating a method of forming a coil according to the present embodiment.

FIG. 5B is a view illustrating the method of forming a coil according to the present embodiment.

FIG. 5C is a view illustrating the method of forming a coil according to the present embodiment.

FIG. 6 is a schematic view schematically illustrating behavior of momentary vibration of a recording disk surface.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.

In the following, the same numeral is given to the same or a similar structural element or member which is illustrated in each of the drawings and redundant description will not be repeated. Then, members of each of the drawings are appropriately enlarged or reduced in scale for easy understandings. Here, in the following description, the lower and the upper in the drawings are respectively expressed as the bottom and the top for convenience.

FIGS. 1A and 1B illustrate a disk drive device 100 according to an embodiment. FIG. 1A is a top view of the disk drive device 100 and FIG. 1B is a side view of the disk drive device 100. Here, FIG. 1A illustrates a state that a top cover 2 is removed. Further, FIG. 2 is a sectional view of a part of the disk drive device 100 according to the present embodiment. Furthermore, FIG. 3 is a sectional view of a hub 4 according to the present embodiment. Each of FIG. 2 and FIG. 3 is the view sectioned at line A-B in FIG. 1A.

The disk drive device 100 includes a chassis 10 which has a base member 3 and a looped circumference wall portion 15, the hub 4 to which a doughnut-shaped recording disk 1 is mounted, a bearing unit 5 which is arranged on the base member 3 so as to rotatably support the hub 4, a spindle drive unit 6 which drives the hub 4 to rotate, a head drive unit 17, the top cover 2, and a screw 9. Further, the disk drive device 100 includes a fixed body portion 7 configured with members which do not rotate and a rotating body portion 8 configured with members which rotate. The fixed body portion 7 and the rotating body portion 8 include the bearing unit 5 which supports the hub 4 to be relatively rotatable and the spindle drive unit 6 which drives the hub 4 to rotate.

The chassis 10 includes the base member 3 which is a plane area of a hollowed portion and the looped circumference wall portion 15 which is formed in a wall shape at the outer circumference of the base member 3. The base member 3 has a bearing hole 3A into which a housing 13, a sleeve 14 and a shaft 16 are inserted. The outer circumference surface of the looped circumference wall portion 15 is formed rectangular. The inner circumference surface of the looped circumference wall portion 15 is formed by connecting a circular portion 15A for surrounding the recording disk 1 and a rectangular portion 15B for surrounding an area to which the head drive unit 17 is mounted. The looped circumference wall portion 15 functions as a support member of the disk drive device 100 for supporting in the rotation axial direction of the shaft 16. On the other hand, the base member 3 functions as a support member of the disk drive device 100 for supporting in the direction perpendicular to the rotation axial direction of the shaft 16.

The top cover 2 which is illustrated in FIG. 1B is arranged and fixed at the upper end of the looped circumference wall portion 15 by screwing the screw 9 with a screw hole 15C which is formed at the upper end surface side of the looped circumference wall portion 15. A clean air room is formed by being enclosed with the chassis 10 and the top cover 2 for covering the hollow portion of the chassis 10. The clean air room is filled with clean air from which particles are removed. The recording disk 1 which is a magnetic recording medium, the rotating body portion 8 and the head drive unit 17 are arranged in the clean air room.

The bearing unit 5 is arranged on the base member 3 and includes the shaft 16, the sleeve 14, the housing 13, an overhanging member 19 and a descent portion 20. Further, the bearing unit 5 includes a radial dynamic pressure groove 22, a thrust dynamic pressure groove 23 and a capillary seal portion 24.

The shaft 16 functions as the rotation axis. The upper end of the shaft 16 is fixed to a shaft hole 4M which is formed at the center of the hub 4. The shaft 16 is inserted into the sleeve 14. The sleeve 14 which is approximately cylindrical is inserted into the housing 13. A part of the outer circumference surface of the sleeve 14 is fixed to the inner circumference surface of the housing 13 by bonding and the like. The overhanging member 19 which overhangs outward in the radial direction is fixed to an opening end surface 14A at the upper side of the sleeve 14. The overhanging member 19 restricts movement of the hub 4 in the axial direction in cooperation with the descent portion 20. Further, the overhanging member 19 and the descent portion 20 prevent the rotating body portion 8 from coming out.

The housing 13 is in the form of a cup with a bottom such that a cylinder portion and a bottom portion are integrally formed. A part of the outer circumference surface of the housing 13 is fixed to the bearing hole 3A which positions approximately at the center of the base member 3. The bottom portion is formed at the lower end of the housing 13 for sealing so that lubricant does not leak to the outside.

The radial dynamic pressure groove 22 and the thrust dynamic pressure groove 23 function as the bearing to rotatably support the hub 4. Two herringbone-shaped radial dynamic pressure grooves 22 are formed to be vertically apart at least at either of the inner circumference surface of the sleeve 14 or the outer circumference surface of the shaft 16. Further, the thrust dynamic pressure grooves 23 which are herringbone-shaped or spiral-shaped are formed at both a surface of the descent portion 20 opposed to the opening end surface of the housing 13 and the upper surface of the descent portion 20 opposed to a lower surface of the overhanging member 19. Here, the thrust dynamic pressure groove 23 may be formed at least at either the opening end surface 14A of the sleeve 14 or the lower end surface 4F of the hub 4 which is opposed to the opening end surface 14A.

When the shaft 16 is rotated, radial dynamic pressure is generated at the lubricant by the radial dynamic pressure groove 22, so that the rotating body portion 8 is supported in the radial direction. Further, when the descent portion 20 is rotated, thrust dynamic pressure is generated at the lubricant by the thrust dynamic pressure groove 23, so that the rotating body portion 8 is supported in the thrust direction.

The capillary seal portion 24 is formed with the inner circumference surface of a cylinder portion of the descent portion 20 and the outer circumference surface of the housing 13 so that the gap between the inner circumference surface of the descent portion 20 and the outer circumference surface of the housing 13 gradually becomes large toward the opening end at the lower side. The lubricant such as oil is infused to a space defined by the radial dynamic pressure groove 22 and the opposing surface thereto, the thrust dynamic pressure groove 23 and the opposing surface thereto, and the capillary seal portion 24. The boundary liquid level at which the lubricant is contacted to outside air is set at some mid-part of the capillary seal portion 24. The capillary seal portion 24 prevents leaking of the lubricant with capillarity.

The spindle drive unit 6 includes a stator core 11 which is fixed to the base member 3, a three-phase coil 12 which is wound around a salient pole of the stator core 11, and an approximate cylindrical magnet 21 which is fixed at an inner cylinder portion 4D of the hub 4.

The stator core 11 includes a circular portion and nine salient poles which are extended in the radial direction therefrom. The stator core 11 is formed by performing insulation coating such as electro-deposition coating and powder coating on the surface thereof after a plurality of magnetic plates such as ferrosilicon plates are laminated. The magnet 21 is formed of rare-earth material such as Nd—Fe—B (neodymium-ferrum-boron), for example. Rustproofing such as electro-deposition coating and spray coating is performed on the surface of the magnet 21. Further, for example, the magnet 21 has driving magnetic poles of twelve poles along the circumferential direction of the inner circumference portion of the magnet 21. The magnet 21 opposes to distal ends of the salient poles.

As the coil 12, a wire 25 is wound predetermined times around the salient pole of the stator core 11 from the lower side, and then, is wound around the adjacent salient pole of the stator core 11 from the upper side. After the wire 25 is continuously wound predetermined times around the salient poles of the stator core 11 in this manner, the wound end of the wire 25 is drawn to the lower side of the salient pole of the stator core 11. Subsequently, the wound end of the wire 25 is drawn to the opposite side of the base member 3 through a wire hole 3B which is disposed at the base member 3, and then, electrically connected to a wiring member 26 which is arranged at the lower surface of the base member 3. The wound end of the drawn wire 25 is fixed with bond so as not to be released. Such fixing prevents the wire 25 from disconnection due to large-amplitude vibration caused by resonance during an ultra-sonic cleaning process. When the coil 12 is powered with three-phase current of approximate sine-waves by a predetermined drive circuit via the wiring member 26, the coil 12 generates a magnetic field for rotation at the salient poles of the stator core 11. Rotation driving force is generated by interaction between the driving poles of the magnet 21 and the magnetic field for rotation, so that the rotating body portion 8 is rotated. Namely, the spindle drive unit 6 drives the rotating body portion 8 to rotate.

The fixed body portion 7 is configured to include the chassis 10 of which section is an approximate hollow shape, the stator core 11, the coil 12, the housing 13 and the sleeve 14. Further, the rotating body portion 8 is configured to include the approximately pan-shaped hub 4 to which the recording disk 1 is mounted, the shaft 16 and the magnet 21.

In the following, the hub 4 is specifically described with reference to FIG. 3. The hub 4 is formed of magnetic material such as SUS43OF which has soft magnetism. It is preferable to form the whole hub 4 with magnetic material in view of generating an effect of magnetic shield. The hub 4 is formed by machining such as pressing and cutting so as to be the predetermined shape of being approximately pan-shaped. For example, stainless of which product name is DHS1 manufactured by Daido Steel Co. Ltd. is preferable in view of less outgassing and easy machining. In addition, stainless of which product name is DHS2 is further preferable in view of excellent corrosion resistance.

The shaft hole 4M is formed at the center of the hub 4 and a circular center portion 4I is formed around the shaft hole 4M. The shaft hole 4M is formed so that the dimension thereof in the axial direction is larger than the dimension in the axial direction of a part of the center portion 4I opposing to the upper end surface of the sleeve 14. A part of the outer circumference of the shaft hole 4M is projected downward. Accordingly, connecting surface between the hub 4 which is thinned and the shaft 16 is ensured.

A circular stepped of two levels is formed at the upper end surface 4A of the hub 4 and the center portion 4I is located at the top level. A recess portion 4J which is lowered downward by one step from the center portion 4I is formed at the top end surface 4A to be ring-shaped. A plurality of threaded holes 4K are disposed at the upper surface of the recess portion 4J at the same circular intervals. A damper 29 is disposed on the recess portion 4J. Then, the circular step between the center portion 4I and the recess portion 4J is fitted to a center hole of the damper 29. The damper 29 is fixed by screwing screws 30 to the threaded holes 4K.

A circular outer cylinder portion 4B is formed as a stepped portion lowered from the periphery of the recess portion 4J. A annular extension portion 4C is formed to extend outward in the radial direction from the lower end of the periphery of the outer cylinder portion 4B. The inner circumference of the center hole of the recording disk 1 is engaged with the outer cylinder portion 4B of the hub 4 so that the recording disk 1 is mounted on the upper surface of the annular extension portion 4C. The annular extension portion 4C sags to the base member 3 side. The outer circumference of the magnet 21 is fixed to the inner cylinder portion 4D. The annular extension portion 4C which is located in an area outside the outer circumference of the magnet 21 in the radial direction functions as a back yoke of the magnet 21.

A circular projecting portion 4E which projects in the direction toward the base member 3 between the housing 13 and the stator core 11 is formed at the lower surface of the hub 4. The circular descent portion 20 is fixed to the inner circumference surface of the circular projecting portion 4E of the hub 4 with bonding.

A lower end surface 4F of the hub 4 opposing to an opening end surface 14A of the sleeve 14 is located at the back surface of the center portion 4I. A portion 4H of the hub 4 opposing to the coil 12 is located at the back surface of the recess portion 4J.

Here, the problem which is recognized by the present inventor is described based on the structure according to the related art which is illustrated in FIG. 4. FIG. 4 is a sectional view of a part of a disk drive device 200 of the related art. When the disk drive device 200 of the related art is thinned, a spindle unit 52 such as a stator core 50 becomes thin accordingly. When the spindle unit 52 becomes thin, the rotation becomes unstable due to torque decrease. When the rotation becomes unstable, the unstableness may impair normal read/write operation of magnetic data at worse.

There may be a solution to use a magnet 54 of which diameter is larger for recapturing the decreased torque. However, with the configuration that the recording disk 1 is located at an area on the extension of the outer circumference of the magnets 54, a back yoke portion 58 of the hub 56 sandwiched by the inner circumference of the recording disk 1 and the outer circumference of the magnet 54 becomes thin in accordance with increase of the diameter of the magnet 54. The back yoke portion 58 constitutes a part of a magnetic circuit through which magnetic flux departing from the outer circumference of the magnet 54. Thus, when the back yoke portion 58 becomes thin, magnetic saturation occurs. When the magnetic saturation occurs, the magnetic flux is hardly increased even though the magnetic field is strengthened. Accordingly, the torque cannot be increased since the increase of the magnetic flux contributing to the torque is slight. On the other hand, the magnetic flux leaking to the recording disk 1 side is extremely increased. Therefore, with the configuration that the recording disk 1 is located at the area on the extension of the outer circumference of the magnet 54, there is a possibility that normal read/write operation of magnetic data is impaired by the leaked magnetic flux. This has been an inhibitor of thinning the disk drive device 200. Further, even in the case that the back yoke portion 58 is thickened in the related art, increase of the torque is not expected since the magnet 54 has to be decreased in size accordingly.

In view of the abovementioned problem, the recording disk 1 according to the present embodiment is arranged at a position to be apart upward from the magnet 21 in the axial direction being away from the area on the extension of the outer circumference of the magnet 21 in the radial direction, as illustrated in FIG. 2. With this configuration, the magnetic flux leaking to the recording disk 1 side can be decreased. Then, the inner cylinder portion 4D of the hub 4 is configured so that the diameter thereof is larger than the diameter of the outer cylinder portion 4B of the hub 4. As a result, it becomes possible to enlarge the outer circumference of the magnet 21 so that the torque is increased due to increase of the magnetic flux amount of the magnetic poles for driving. Accordingly, the configuration is preferable for the thinned disk drive device 100. Further, since the recording disk 1 is arranged at the upper position in the axial direction being away from the area on the extension of the outer circumference of the magnet 21 in the radial direction, the back yoke of the hub 4 can be configured to be sufficiently thick in the radial direction. As a result, even in the case that the magnet 21 of which energy product is larger is used, affecting of the leaked magnetic flux can be suppressed and the torque can be increased.

The diameter of a circle connecting the salient ends of the stator core 11 may be set to be 80% or more of the diameter of the outer cylinder portion 4B of the hub 4. By configuring the stator core 11 to be large as mentioned above, more winding can be performed for the coil 12 so that torque increase is expected. Here, when the diameter of the circle connecting the salient ends of the stator core 11 exceeds 100% of the diameter of the outer cylinder portion 4B, the leaked magnetic flux of the magnet 21 may affect the recording disk 1 and may impair the normal read/write operation of magnetic data. Therefore, the diameter of the circle connecting the salient ends of the stator core 11 is within a range of 80% to 100% of the diameter of the outer cylinder portion 4B.

The base member 3 has a wire hole 3B through which the wire 25 for forming the coil 12 is inserted. A drawing line of the wire 25 which forms the coil 12 is introduced to exit through the wire hole 3B to the back surface 3C of the upper surface of the base member 3 on which the bearing unit 5 is arranged. In the related art of FIG. 4, the drawing line of the wire is connected to a wiring member 66 by soldering at a position strictly below the position where the drawing line is drawn from the coil 12. The thickness of the wiring member 66 and the height of the connection portion 68 at the position strictly below the coil 62 are to be a barrier of thinning the spindle drive unit 5.

In view of the abovementioned, the drawing line of the wire 25 is introduced to exit through the wire hole 3B to the back surface 3C of the upper surface of the base member 3 on which the bearing unit 5 is arranged, and electrically connected to the wiring member 26 at the outer side of the outer diameter of the magnet 21 in the radial direction, as illustrated in FIG. 2. Namely the drawing line of the wire 25 is guided via the wire hole 3B to the back of the base member surface on which the stator core is arranged, and is connected to a wiring member 26 at a position outside the outer diameter of the magnet 21 in the radial direction. Thus, the spindle drive unit 6 can be thinned by the amount of the height of connection portion 26A between the drawing line and the wiring member 26. Here, the base member 3 at an area outside the magnet 21 in the radial direction can be formed thin since members to be arranged on the base member 3 is less than the area to which the spindle drive unit 6 is arranged. The connection portion 26A can be arranged at the thinned area of the base member 3.

Here, there is a case that the base member 3 is formed of metal such as aluminum. In this case, there is a possibility that the wire 25 which is drawn to the lower surface 3C of the base member 3 is electrically short-circuited by directly contacting to the base member 3. In order to cope with this problem, a channel portion 3D which introduces the wire to exit through the wire hole 3B for connecting to the wiring member 26 is disposed at the back surface 3C of the surface of the base member 3 to which the bearing unit 5 is disposed. The channel portion 3D is insulation treated. As a result, the problem that the wire 25 is electrical short-circuited with the base member 3 is relieved. Further, by combining the positioning of the abovementioned connection portion 26A with the configuration of positioning outside the magnet 21 in the radial direction, the spindle drive unit 6 can be thinned by the amount based on the thickness of the wiring member 66 and the height of the connection portion 68 of the related art which is illustrated in FIG. 4. Here, for example, cationic electro-deposition coating (hereinafter, called ED coating) onto the base member 3 which is molded with aluminum die-casting is preferable as the isolation process in view of less pin holes.

Here, when the disk drive device 100 is configured to be further thinned, the coil 12 which is wound around the salient poles and the lower surface of the hub 4 become extremely close. In this case, the possibility that the coil 12 is contacted to the rotating hub 4 is increased. When the coil 12 is contacted to the hub 4, electrical short-circuit may occur. In order to cope with this problem, the coil 12 is leveled so that the surface opposing to the hub 4 and the surface opposing to the base member 3 are to be flat.

FIGS. 5A to 5C illustrate a forming method of the coil 12 according to the present embodiment. FIG. 5A illustrates the coil 12 before forming, FIG. 5B illustrates the coil 12 during pressing, and FIG. 5C illustrates the coil 12 after pressing. As illustrated in the drawings, the coil 12 is formed by being pressed between a first pressing die 40 and a second pressing die 42 after the wire 25 is wound around the salient poles of the stator core 11. The pressing surfaces of the first pressing die 40 and the second pressing die 42 are flat. By forming the coil 12 to be flat with pressing, the dimension of the coil 12 in the axial direction is stabilized so that the possibility that the coil 12 is contacted to the rotating hub 4 can be decreased. Accordingly, the dimension of the coil 12 in the axial direction can be thinned.

Further, in order to cope with the contacting problem of the coil 12 to the rotating hub 4, the flattening ratio of the wire 25 which forms the leveled coil 12 may be 90% or less. The flattening ratio of the wire 25 is expressed by a percentage of the dimension “b” of the section of the single wire 25 in the axial direction against the dimension “a” in the radial direction. Here, the flattening ratio of the wire 25 of the coil 12 is defined at a part of which flattening ratio is the lowest. The equation thereof is as follows.

The flattening ratio of the wire 25=(b/a)×100

When the coil 12 is formed with pressing so as to limit the dimension of the coil 12 in the axial direction, the part of the wire 25 of which flattening ratio becomes lowest is the part which is thickest in the axial direction. As a result, the contacting possibility of the coil 12 to the rotating hub 4 is further decreased.

Furthermore, in order to cope with the contacting problem of the coil 12 to the rotating hub 4, it is also possible to perform the insulation treat on the surface of the hub 4 opposing to the coil 12. As a result, the possibility of the electrical short-circuiting to cause a malfunction is decreased. For example, a circular film 27 which is made of Polyethylene terephthalate (PET) may be stuck with double-faced tape to the surface of the hub 4 opposed to the coil 12. This method is preferable in view of easy operation.

Further, there may be a problem that electrical short-circuit occurs due to contacting of the coil 12 to the base member 3. In order to cope with this problem, it is also possible to perform an insulation treat on the surface of the base member 3 opposed to the coil 12. As a result, the possibility that the coil 12 is contacted to the base member 3 to cause the electrical short-circuit is decreased. For example, it is also possible to perform the ED coating on the base member 3 which is molded with aluminum die-casting as the insulation treat. This is preferable in view of less pin holes. Further, a circular film 28 which is made of PET may be stuck with double-faced tape to the surface of the base member 3 opposing to the coil 12. This method is preferable in view of easy operation.

By the way, in the case that the disk drive device 100 is thinned, stiffness is decreased and rocking-mode resonance frequency is decreased when the portion 4H of the hub 4 opposed to the coil 12 in the axial direction is shortened. Here, the rocking-mode resonance is described with reference to FIG. 6. FIG. 6 is a schematic view which schematically illustrates behavior of momentary vibration of a recording disk 1 surface. In FIG. 6, dashed lines illustrate a nodal diameter 36 and a nodal circle 38 at the vicinity of toque-ripple frequency. The area with hatching indicates that the vibration phase thereof at the vicinity of the torque-ripple frequency is reverse to that of the area without hatching. Solid lines are contour lines of vibration displacement at the vicinity of the torque-ripple frequency.

The resonance of the disk drive device 100 during non-rotating has been examined in the state that the recording disk 1 is mounted in the disk drive device 100. As a result, the rocking-mode resonance with the single nodal diameter 36 and the nodal circle 38 as an intermediate portion was observed in the recording disk 1 at the vicinity of the torque-ripple frequency. Through the study of the present inventor, the main factors which determine the frequency of the rocking-mode resonance are discovered to be the stiffness of the bearing, the stiffness of the connecting portion between the hub 4 and the shaft 16, the stiffness of the connecting portion between the recording disk 1 and the hub 4, the stiffness of the recording disk 1 itself, the lateral moment of inertia of the recording disk 1, and the lateral moment of inertia of the hub 4.

When the frequency of the rocking-mode resonance becomes low, there may be a case that large vibration occurs due to resonance with the variation of the drive torque. There may be a problem that such vibration causes a malfunction of normal read/write operation of magnetic data at worse. In order to cope with this problem, the width in the axial direction of the hub 4 opposed to the coil 12 may be larger than the width in the axial direction of the base member 3 opposed to the coil 12. This is for the relative relation of dimensions of the base member 3 and the hub 4 in the axial direction in the case that the disk drive device 100 is thinned. As a result, the problem caused by decrease of the frequency of the rocking-mode resonance is relieved.

Next, in the disk drive device 200 of the related art which is illustrated in FIG. 4, a center part of a damper 70 is fixed at the center of the shaft 74 with a screw 72. Therefore, the center part of the hub 56 is to be thinned in the axial direction by the amount of the damper 70 and the screw 72. When the center part of the hub 56 is thinned in the axial direction, the frequency of rocking-mode resonance becomes low. Accordingly, there may be a case that large vibration occurs due to the resonance with the variation of the drive torque.

In order to cope with this problem, in the disk drive device 100 according to the present embodiment, the hub 4 includes the recess portion 4J which is formed on the surface of the hub 4 at the side to which the recording disk 1 is mounted and the threaded hole 4K which is formed at the recess portion 4J, as illustrated in FIG. 2 and FIG. 3. The damper 29 is fixed to the threaded hole 4K with the screw 30. As a result, the problem caused by thinning the center portion 4I of the hub 4 in the axial direction is relieved. In addition, since the shaft 16 can be configured to be long, it is preferable because decrease of the bearing stiffness can be prevented.

Further, there may be a case that the dimension in the axial direction of the thread portion of the threaded hole 4K which is formed at the hub 4 is insufficient. In order to cope with this problem, the threaded portion 4K is formed to penetrate in the axial direction. Further, a cover member 31 is disposed at the surface of the hub 4 to which the threaded portion 4K is formed and which is opposed to the coil 12. As a result, the problem that the dimension in the axial direction of the thread portion of the threaded hole 4K is insufficient is relieved. A variety of materials can be used for the cover member 31. For example, a PET film may be stuck with double-faced tape to the surface of the base member 3 opposed to the coil 12. This method is preferable in view of easy operation as well as functioning as the insulation treat against the coil 12.

Next, in the disk drive device 200 of the related art which is illustrated in FIG. 4, a cylinder portion 76 and a bottom portion 78 of the housing is fixed by bonding as separate members. In this case, when the disk drive device is thinned, the bonding part also becomes thin. When the bonding part becomes thin, the connection strength is decreased. Accordingly, there is a possibility of disconnection due to impact.

In order to cope with this problem, in the disk drive device 100 of the present embodiment, the housing 13 is in the form of a cup with a bottom such that a cylinder portion and a bottom portion are integrally formed, as illustrated in FIG. 2. As a result, the problem of disconnection between the cylinder portion and the bottom portion of the housing 13 is relieved even when the disk drive device 100 becomes thin.

Next, in the disk drive device 200 of the related art which is illustrated in FIG. 4, a circular member 80 is fixed by bonding to the inner circumference of a circular projecting portion of the hub 56. The doughnut-shaped circular member 80 is formed so that the dimension thereof in the axial direction is 1.2 mm or more for ensuring connection strength with the hub 56. When the disk drive device 200 becomes thin, the center portion of the hub 56 in the axial direction is to be thin by the amount of the circular member 80. When the center portion of the hub 56 in the axial direction becomes thin, the frequency of the rocking-mode resonance becomes low. Accordingly, there may be a case that large vibration occurs due to resonance with the variation of the drive torque.

In order to cope with this problem, the bearing unit 5 of the present embodiment includes the descent portion 20 which is rotated integrally with the hub 4 and the overhanging member 19 which is arranged so as to be nonrotatable at a position opposed to the descent portion 20 in the axial direction, as illustrated in FIG. 2. Further, it is also possible that the descent portion 20 restricts movement of the hub 4 in cooperation with the overhanging member 19 and the width in the axial direction of the descent portion 20 opposed to the overhanging member 19 is set to be 0.6 mm or less. Namely, the thickness of a disk portion 20A of the descent portion 20 is set to be 0.6 mm or less. As a result, in the case that the disk drive device 100 is thinned, the dimension of the center portion 4I of the hub 4 in the axial direction can be ensured. In addition, it is preferable that the dimension of the descent portion 20 is set to be 0.4 mm or less because the center portion 4I of the hub 4 can be further thickened in the axial direction.

Further, when the circular member 80 of FIG. 4 is thinned in the axial direction, there may be a problem of disconnection due to impact since the connection strength of the circular member 80 with the hub 56 is decreased. In order to cope with this problem, the descent portion 20 is formed by integrating the disk portion 20A which is opposed to the overhanging member 19 in the axial direction and a cylinder portion 20B which is connected to the periphery portion of the disk portion 20A. With this configuration, the dimension in the axial direction for connecting to the circular projecting portion 4E can be sufficiently ensured. As a result, the problem of disconnection between the descent portion 20 and the hub 4 is relieved. For example, by setting the dimension of the cylinder portion 20B in the axial direction to be 2.0 mm or more, the connection strength with the hub 4 is sufficiently ensured. In addition, by setting the dimension of the disk portion 20A in the axial direction to be 0.4 mm or less thereafter, the dimension of the center portion 4I of the hub 4 can be configured to be thick in the axial direction.

There may be a problem that the machining of the descent portion 20 requires much expense in time. In order to cope with this problem, the descent portion 20 may be formed by pressing of metal material. As a result, the problem of machining expense of the descent portion 20 in time can be relieved.

Further, the thrust dynamic pressure groove 23 may be formed at least at any surface of the disk portion 20A of the descent portion 20. Specifically, the thrust dynamic pressure groove 23 is formed at least either at the surface of the disk portion 20A opposed to the opening upper end surface of the housing 13 or the surface of the disk portion 20A opposed to the overhanging member 19. As a result, machining of the thrust dynamic pressure groove 23 becomes easy.

Here, in accordance with thinning of the disk drive device 100, the stator core 11 is configured to be thin. When the stator core 11 becomes thin, there is a possibility that the stator core 11 is attached to be inclined when the circular portion thereof is fitted to the base member 3. In order to cope with this problem, a stator core supporting member 32 is disposed between the salient pole of the stator core 11 and the base member 3. The stator core supporting member 32 is arranged to circularly project from the base member 3 toward the salient pole of the stator core 11 at which the coil 12 is not arranged. As a result, the stator core 11 is supported at the inner circumference and the outer circumference. Accordingly, the problem of the stator core 11 inclining by the thinning is relieved.

Further, the stator core supporting member 32 is formed integrally with the base member 3. This is preferable in view of saving assembling time. On the contrary, it is also possible that the stator core supporting member 32 is arranged as a separate member from the base member 3. This is preferable because the stator core supporting member 32 can be formed of a variety of materials such as metal material and plastic material.

A part of the hub 4 covering the outer circumference of the magnet 21 performs a function of so-called back yoke. When the back yoke becomes thin, the magnetic resistance is increased. When the magnetic resistance is increased, the magnetic flux which is generated by the magnet 21 is decreased. When the magnetic flux is decreased, the torque is decreased. Accordingly, there may be a problem that a malfunction such as unstable rotation occurs. In order to cope with this problem, the hub 4 has the annular extension portion 4C which extends outward and the diameter of the outer circumference end of the annular extension portion 4C is set to be larger than the diameter of the inner cylinder portion 4D of the hub 4 by 4 mm or more. As a result, the thickness of the back yoke is sufficiently ensured and the problem caused by the torque decrease is relieved.

Here, when strong magnetic material is used for increasing the torque, there is a case that leaked magnetic flux is increased due to magnetic saturation in the back yoke. When the leaked magnetic flux is increased, a noise signal may be generated at a magnetic head for reading/writing data. When the noise signal is large, there is a possibility that normal operation of reading/writing of magnetic data is impaired. In order to cope with this problem, the saturation magnetic flux density of the annular extension portion 4C which functions as the back yoke is set to be 1 T (tesla) or more. With this configuration, the saturation magnetic flux density can be sufficiently ensured at the back yoke and the problem of increasing of the leaked magnetic flux is relieved. Here, when the saturation magnetic flux density of the hub 4 is set to be 1.2 T or more, stronger magnetic material can be used.

Here, there may be a demand to increase the torque so as to stabilize the rotation. In order to cope with this demand, the opposing clearance between the distal end of the salient pole and the magnet 21 is set to be 0.4 mm or less. Namely, a gap where the distal end of the salient pole and the magnet 21 face each other is set to be 0.4 mm or less. As a result, an air gap of the magnetic circuit becomes small and the magnetic flux amount of the magnet 21 is increased so that the torque is increased. The opposing clearance between the salient pole and the magnet 21 is preferable to be 0.4 mm or less in view of ensuring effect to increase the torque and to be 0.2 mm or more in view of preventing contact between the salient pole and the magnet 21.

Further, the maximum energy product of the magnet 21 according to the present embodiment may be set to be 10 megagauss-oersted (MGOe) or more. Accordingly, the magnetic flux amount of the magnet 21 is increased so that the torque is increased. The maximum energy product of the magnet 21 is preferably to be 10 MGOe or more in view of ensuring the torque increasing effect and to be 16 MGOe or less in view of easiness of magnetizing. Here, by combining the magnet 21 of the abovementioned maximum energy product with the back yoke of which saturation magnetic density is 1 T or more, the leaking of the magnetic flux from the back yoke can be suppressed even in the thinned disk drive device 100.

There is a demand of further thinning and lightening for the disk drive device 100 which is mounted on a portable apparatus. In order to cope with this demand, the inner diameter of the recording disk 1 is set to be 20 mm and the thickness of the disk drive device in the axial direction is set to be 7.5 mm or less. As a result, the portable apparatus can be configured to be thin and light. Further, it also contributes to resources saving.

As described above, the disk drive device 100 according to the present embodiment can stabilize the rotation of the recording disk 1 while achieving further thinning so as to be a preferable shape for a portable apparatus and the like.

Not limited to the abovementioned embodiments, the present invention is possible to be modified by various design changes based on knowledge of skilled persons. The configuration illustrated in each of the drawings is simply for describing an example and can be appropriately modified so that the similar effects are obtained as long as the similar functions can be achieved. 

1. A disk drive device comprising: a base member; a hub; a bearing unit which is arranged on the base member and which rotatably supports the hub; and a spindle drive unit which drives the hub to rotate, wherein the spindle drive unit includes a stator core having a salient pole, a coil which is wound around the salient pole, and a magnet which is opposed to the salient pole; the hub formed of magnetic material includes an outer cylinder portion which is engaged with an inner circumference of a recording disk, and an inner cylinder portion to which an outer circumference of the magnet is fixed; and the diameter of the inner cylinder portion is larger than the diameter of the outer cylinder portion.
 2. The disk drive device according to claim 1, wherein the diameter of a circle connecting salient ends of the stator core is 80% or more of the diameter of the outer cylinder portion of the hub.
 3. The disk drive device according to claim 1, wherein the base member includes a wire hole through which a wire for forming the coil is passing; and the wire is guided via the wire hole to the back of the base member surface on which the stator core is arranged, and is connected to a wiring member at a position outside the outer diameter of the magnet in the radial direction.
 4. The disk drive device according to claim 1, wherein a channel portion which guides the wire via the wire hole for connecting to the wiring member at the back of the base member surface on which the stator core is arranged; and the channel portion is insulation treated.
 5. The disk drive device according to claim 1, wherein a surface of the coil opposed to the hub and a surface of the coil opposed to the base member are leveled.
 6. The disk drive device according to claim 5, wherein the flattening ratio of the wire which forms the leveled coil is 90% or less.
 7. The disk drive device according to claim 1, wherein a surface of the hub opposed to the coil is insulation treated.
 8. The disk drive device according to claim 1, wherein a surface of the base member opposed to the coil is insulation treated.
 9. The disk drive device according to claim 1, wherein width in the axial direction of the hub opposed to the coil is larger than width in the axial direction of the base member opposed to the coil.
 10. The disk drive device according to claim 1, wherein the hub includes a recess portion on a surface of the side to which the recording disk is mounted and a threaded hole which is formed at the recess portion.
 11. The disk drive device according to claim 10, wherein the threaded portion is formed to penetrate in the axial direction; and a cover member is disposed at a surface of the hub to which the threaded portion is formed and which is opposed to the coil.
 12. The disk drive device according to claim 1, wherein the bearing unit includes a shaft, a sleeve into which the shaft is inserted and a housing into which the sleeve is inserted; and the housing is in the form of a cup with a bottom such that a cylinder portion and a bottom portion are integrally formed.
 13. The disk drive device according to claim 1, wherein the bearing unit further includes a descent portion which is rotated integrally with the hub and a overhanging member which is arranged so as to be nonrotatable at a position opposed to the descent portion in the axial direction; the descent portion restricts movement of the hub in the axial direction in cooperation with the overhanging member; and width in the axial direction of the descent portion opposed to the overhanging member is 0.6 mm or less.
 14. The disk drive device according to claim 13, wherein the descent portion is formed by integrating a disk portion which is opposed to the overhanging member in the axial direction and a cylinder portion which is connected to the periphery of the disk portion.
 15. The disk drive device according to claim 14, wherein a thrust dynamic pressure groove is formed at least at any surface of the disk portion of the descent portion.
 16. The disk drive device according to claim 1, wherein a stator core supporting member is disposed between the salient pole of the stator core and the base member.
 17. The disk drive device according to claim 1, wherein the hub includes a annular extension portion which extends outward; and the diameter of the annular extension portion is larger than the diameter of the inner cylinder portion by 4 mm or more.
 18. The disk drive device according to claim 1, wherein saturation magnetic flux density of the hub is set to be 1 T or more.
 19. The disk drive device according to claim 1, wherein a gap where the salient pole and the magnet face each other is set to be 0.4 mm or less.
 20. The disk drive device according to claim 1, wherein maximum energy product of the magnet is set to be 10 MGOe or more. 